For example, EP 1 306 665 A2 discloses an optical instrument for measuring polarization-dependent properties which comprises a light source in the EUV or X-radiation region and a rotatable polarizer. The polarizer is substantially comprised of a set of mirrors that reflects the incident light at least three times. The mirrors are arranged in such a way that the optical axes of the incident and emergent light are on the same straight line.
A beam splitter is among other things known from US 2003/0142322 A1; it splits light in the EUV region by means of a diffraction grating into transmitted light and reflected light, the transmitted and the reflected light being polarized orthogonally.